Ernst Regener

Ernst Regener sank instruments down to a depth of 230 m. in Lake Constance, and sent up self-registering apparatus in balloons up to 27 km. in the atmosphere. Regener inferred that the cosmic radiation carried a flux of energy equal to 3.5*10^-3 erg/sec /cm^2, which is the same order of magnitude as the energy arriving at the earth from the stars in the form of light and heat.

The flux referred to here is that of high energy radiation--i.e. positrons. Not that of low frequency photons making up the cosmic background radiation first discovered experimentally by Penzias and Wilson.

Regener predicted a 2.8 K cosmic background radiation.

Sources

Relativity Gravitation and World Structure (1935) -- Alfred Edward Milne